Methods and devices for use of degassed fluids with fluid enhanced ablation devices

ABSTRACT

Devices, systems, and methods for degassing fluid prior to applying fluid to a treatment site during ablation therapy are provided. In one embodiment, an ablation system can include an elongate body, an ablation element, a heating assembly, and a fluid source. Fluid in the fluid source can be at least partially degassed prior to being provided as part of the system, or, in some embodiments, a degassing apparatus can be provided that can be configured to degas fluid within the system prior to applying the fluid to the treatment site. The degassing apparatus can include one or more gas-permeable and fluid-impermeable tubes disposed therein, which can allow gas to be removed from fluid passing through the apparatus. Other exemplary devices, systems, and methods are also provided.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser.No. 61/474,574, filed on Apr. 12, 2011, and entitled “Improvement inAblation Catheters.” This application is also related to U.S.application Ser. No. 13/445,034 entitled “Devices and Methods for RemoteTemperature Monitoring in Fluid Enhanced Ablation Therapy,” U.S.application Ser. No. 13/445,036 “Methods and Devices for Heating Fluidin Fluid Enhanced Ablation Therapy,” U.S. application Ser. No.13/445,373 “Methods and Devices for Controlling Ablation Therapy,” andU.S. application Ser. No. 13/445,365 “Devices and Methods for ShapingTherapy in Fluid Enhanced Ablation,” respectively, and filedconcurrently with the present application. The disclosures of each ofthese applications are hereby incorporated by reference in theirentirety.

GOVERNMENT RIGHTS

This invention was made with government support under grants CA69926 andHL63535 awarded by The National Institutes of Health. The government hascertain rights in the invention.

FIELD

The invention relates generally to fluid enhanced ablation, such as theSERF™ ablation technique (Saline Enhanced Radio Frequency™ ablation),and more particularly relates to methods and devices for degassing fluidintroduced into tissue during fluid enhanced ablation.

BACKGROUND

The use of thermal energy to destroy bodily tissue can be applied to avariety of therapeutic procedures, including the destruction of tumors.Thermal energy can be imparted to the tissue using various forms ofenergy, such as radio frequency electrical energy, microwave or lightwave electromagnetic energy, or ultrasonic vibrational energy. Radiofrequency (RF) ablation, for example, can be effected by placing one ormore electrodes against or into tissue to be treated and passing highfrequency electrical current into the tissue. The current can flowbetween closely spaced emitting electrodes or between an emittingelectrode and a larger, common electrode located remotely from thetissue to be heated.

One disadvantage with these techniques is that maximum heating oftenoccurs at or near the interface between the therapeutic tool and thetissue. In RF ablation, for example, maximum heating can occur in thetissue immediately adjacent to the emitting electrode. This can reducethe conductivity of the tissue, and in some cases, can cause waterwithin the tissue to boil and become water vapor. As this processcontinues, the impedance of the tissue can increase and prevent currentfrom entering into the surrounding tissue. Thus, conventional RFinstruments are limited in the volume of tissue that can be treated.

Fluid enhanced ablation therapy, such as the SERF™ ablation technique(Saline Enhanced Radio Frequency™ ablation), can treat a greater volumeof tissue than conventional RF ablation. The SERF ablation technique isdescribed in U.S. Pat. No. 6,328,735, which is hereby incorporated byreference in its entirety. Using the SERF ablation technique, saline ispassed through a needle and heated, and the heated fluid is delivered tothe tissue immediately surrounding the needle. The saline helpsdistribute the heat developed adjacent to the needle and thereby allowsa greater volume of tissue to be treated with a therapeutic dose ofablative energy. The therapy is usually completed once a target volumeof tissue reaches a desired therapeutic temperature, or otherwisereceives a therapeutic dose of energy.

One problem that can arise in fluid enhanced ablation therapy is thatgas dissolved in the fluid can come out of solution due to heating thatoccurs before or during its introduction into the volume of tissue to betreated. When gas comes out of solution, it introduces a compressiblegas into a system otherwise filled with an incompressible fluid. Thecompliance of the compressible gas can introduce a number ofcomplications into the fluid enhanced ablation system and, as the amountof compliance in the system increases, the efficiency and effectivenessof the treatment can decrease. For example, bubbles formed from gascoming out of solution in the fluid (e.g., as the result of localizedsuper-heating of the fluid near an RF electrode) can affect the fluidflow rate since the gas bubbles are compressible and can absorb pressurecreated by a fluid pump. Variance in the fluid flow rate can, in turn,reduce the volume of tissue that can be treated and make ablationtherapy less reliable and reproducible. Still further, introducing gasbubbles into tissue within the body can, in some circumstances, haveunintended and undesirable medical consequences for a patient.

Accordingly, there remains a need for improved devices and methods forfluid enhanced ablation therapy.

SUMMARY

Devices, systems, and methods are generally provided for improvingablation therapy by degassing fluid provided in conjunction with suchtherapy. In one embodiment of an ablation system, the system can includean elongate body, an ablation element, a heating assembly, and a fluidsource. The elongate body can have proximal and distal ends, an innerlumen extending through the elongate body, and at least one outlet portformed in the elongate body and configured to deliver fluid to tissuesurrounding the elongate body. The ablation element can be disposedalong a length of the elongate body adjacent to the at least one outletport, and it can be configured to heat tissue surrounding the ablationelement when the elongate body is inserted into tissue. The heatingassembly can be disposed within the inner lumen, adjacent to theablation element, and it can be configured to heat fluid flowing throughthe inner lumen. The fluid source can be in fluid communication with theinner lumen such that fluid can be delivered from the fluid source andthrough the inner lumen. The fluid source can contain a volume of fluidthat is at least partially degassed such that the fluid contains one ormore gases having a predetermined pressure and mixture.

A pump can be coupled to the fluid source and it can be configured topump fluid from the fluid source and through the inner lumen of theelongate body. In some embodiments, a mass exchanger can be coupled tothe fluid source and it can be configured to at least partially degasthe fluid of the fluid source. The fluid source can include a syringethat is configured to couple to the elongate body for delivering fluidto the inner lumen. In some embodiments, the fluid can be saline.Further, a sensor can be included as part of the system. The sensor canbe configured to measure an amount of gas in the fluid.

In another exemplary embodiment of an ablation system, the system caninclude an elongate body, an ablation element, a heating assembly, and amass exchanger. The elongate body can have proximal and distal ends, aninner lumen extending through the elongate body, and at least one outletport formed in the elongate body and configured to deliver fluid totissue surrounding the elongate body. The ablation element can bedisposed along a length of the elongate body adjacent to the at leastone outlet port, and it can be configured to heat tissue surrounding theablation element when the elongate body is inserted into tissue. Theheating assembly can be disposed within the inner lumen, adjacent to theablation element, and it can be configured to heat fluid flowing throughthe inner lumen. The mass exchanger can be in fluid communication withfluid flowing through the inner lumen, and further, it can be configuredto at least partially degas fluid flowing through the inner lumen.

The mass exchanger can include a plurality of gas-permeable andfluid-impermeable tubes, as well as at least one outlet configured tocouple to a gas source for adjusting the amount of gas in the fluidflowing through the plurality of gas-permeable and fluid-impermeabletubes. The gas source can include a vacuum source for removing gas fromthe fluid. Alternatively, the gas source can include one or more gaseshaving a predetermined pressure and mixture. The mass exchanger can bedisposed proximal of the heating assembly such that fluid is at leastpartially degassed before being heated by the heating assembly. In someembodiments, the mass exchanger can be disposed within a control unitcoupled to a proximal end of the elongate body. The control unit caninclude a pump that is effective to pump fluid from a fluid source,through the mass exchanger, and into the inner lumen of the elongatebody. The system can further include a sensor that can be configured tomeasure an amount of a gas in fluid after it flows through the massexchanger.

Methods for ablating tissue are also provided, and in one exemplaryembodiment, the method can include inserting an elongate body into atissue mass, delivering fluid that is at least partially degassedthrough an inner lumen of the elongate body, delivering energy to atleast one heating assembly disposed within the inner lumen to heat theat least partially degassed fluid within the lumen, and deliveringenergy to an ablation element. The at least partially degassed fluid cancontain one or more gases having a predetermined pressure and mixture.The fluid can flow through at least one outlet port in the elongate bodyand into the tissue mass. Further, delivering energy to an ablationelement can occur simultaneously with delivering energy to the at leastone heating assembly, to ablate the tissue mass.

In some embodiments, prior to delivering the at least partially degassedfluid through the inner lumen, a pump can be activated to deliver fluidthrough a mass exchanger. The mass exchanger can at least partiallydegas the fluid, and the at least partially degassed fluid can flow fromthe mass exchanger and into the inner lumen of the elongate body.Delivering the at least partially degassed fluid through an inner lumencan include injecting the at least partially degassed fluid into acontrol unit and activating a pump to cause the pump to force the atleast partially degassed fluid through the inner lumen. The fluid caninclude saline. Further, in some embodiments, prior to delivering atleast partially degassed fluid through the inner lumen of the elongatebody, a sensor can be operated to determine an amount of a gas in the atleast partially degassed fluid.

In another aspect, a method for ablating tissue is provided thatincludes contacting a tissue mass with an ablation element having atleast one outlet port formed thereon, and delivering fluid through theat least one outlet port, where the fluid is at least partially degassedsuch that the fluid contains one or more gases having a predeterminedpressure and mixture. The method further includes delivering energy tothe ablation element to ablate the tissue mass.

BRIEF DESCRIPTION OF DRAWINGS

This invention will be more fully understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a diagram of one embodiment of a fluid enhanced ablationsystem;

FIG. 2 is a perspective view of one embodiment of a medical devicehaving an elongate body for use in fluid enhanced ablation;

FIG. 3 is a graphical representation of simulated heating profiles forvarious forms of ablation;

FIG. 4 is a graphical representation of performance profiles for varioustypes of saline at different temperatures and supplied powers;

FIG. 5 is a perspective view of one exemplary embodiment of a massexchanger for use in conjunction with a fluid enhanced ablation system;

FIG. 6 is a side, semi-transparent view of the mass exchanger of FIG. 5having a vacuum source coupled thereto; and

FIG. 7 is a side, semi-transparent view of the mass exchanger of FIG. 5having a gas source coupled thereto.

DETAILED DESCRIPTION

Certain exemplary embodiments will now be described to provide anoverall understanding of the principles of the structure, function,manufacture, and use of the devices and methods disclosed herein. One ormore examples of these embodiments are illustrated in the accompanyingdrawings. Those skilled in the art will understand that the devices andmethods specifically described herein and illustrated in theaccompanying drawings are non-limiting exemplary embodiments and thatthe scope of the present invention is defined solely by the claims. Thefeatures illustrated or described in connection with one exemplaryembodiment may be combined with the features of other embodiments. Suchmodifications and variations are intended to be included within thescope of the present invention.

The terms “a” and “an” can be used interchangeably, and are equivalentto the phrase “one or more” as utilized in the present application. Theterms “comprising,” “having,” “including,” and “containing” are to beconstrued as open-ended terms (i.e., meaning “including, but not limitedto,”) unless otherwise noted. The terms “about” and “approximately” usedfor any numerical values or ranges indicate a suitable dimensionaltolerance that allows the composition, part, or collection of elementsto function for its intended purpose as described herein. These termsgenerally indicate a ±10% variation about a central value. Componentsdescribed herein as being coupled may be directly coupled, or they maybe indirectly coupled via one or more intermediate components. Therecitation of any ranges of values herein is merely intended to serve asa shorthand method of referring individually to each separate valuefalling within the range, unless otherwise indicated herein, and eachseparate value is incorporated into the specification as if it wereindividually recited. Further, to the extent that linear or circulardimensions are used in the description of the disclosed devices,systems, and methods, such dimensions are not intended to limit thetypes of shapes that can be used in conjunction with such devices,systems, and methods. A person skilled in the art will recognize that anequivalent to such linear and circular dimensions can easily bedetermined for any geometric shape.

All methods described herein can be performed in any suitable orderunless otherwise indicated herein or otherwise clearly contradicted bycontext. The use of any and all examples, or exemplary language (e.g.,“such as”), provided herein is intended merely to better illuminate theinvention and does not impose a limitation on the scope of the inventionunless otherwise claimed. No language in the specification should beconstrued as indicating any non-claimed element as essential to thepractice of the invention. Further, to the extent the term “saline” isused in conjunction with any embodiment herein, such embodiment is notlimited to use of “saline” as opposed to another fluid unless explicitlyindicated. Other fluids can typically be used in a similar manner. Stillfurther, to the extent the term “degas” or “degassing” is used herein,such term is meant to include any amount of degassing, including theremoval of a small amount of one or more gases from the fluid or theremoval of all of one or more gases from the fluid.

Fluid Enhanced Ablation Systems

The present invention is generally directed to degassed fluids used inconjunction with fluid enhanced ablation devices and treatments. Fluidenhanced ablation, as mentioned above, is defined by passing a fluidinto tissue while delivering therapeutic energy from an ablationelement. The delivery of therapeutic energy into tissue can causehyperthermia in the tissue, ultimately resulting in necrosis. Thistemperature-induced selective destruction of tissue can be utilized totreat a variety of conditions including tumors, fibroids, cardiacdysrhythmias (e.g., ventricular tachycardia, etc.), and others.

Fluid enhanced ablation, such as the SERF™ ablation technique (SalineEnhanced Radio Frequency™ ablation) described in U.S. Pat. No. 6,328,735and incorporated by reference above, delivers fluid heated to atherapeutic temperature into tissue along with ablative energy.Delivering heated fluid enhances the ablation treatment because thefluid flow through the extracellular space of the treatment tissue canincrease the heat transfer through the tissue by more than a factor oftwenty. The flowing heated fluid therefore convects thermal energy fromthe ablation energy source further into the target tissue. In addition,the fact that the fluid is heated to a therapeutic temperature increasesthe amount of energy that can be imparted into the tissue. The fluid canalso be at least partially degassed, which can further enhance theeffectiveness of the fluid application as described below. Finally, thefluid can also serve to constantly hydrate the tissue and prevent anycharring and associated impedance rise.

FIG. 1 illustrates a diagram of one exemplary fluid ablation system 100.The system includes an elongate body 102 configured for insertion into atarget volume of tissue. The elongate body can have a variety of shapesand sizes according to the geometry of the target tissue. Further, theparticular size of the elongate body can depend on a variety of factorsincluding the type and location of tissue to be treated, the size of thetissue volume to be treated, etc. By way of example only, in oneembodiment, the elongate body can be a thin-walled stainless steelneedle between about 16- and about 18-gauge (i.e., an outer diameter ofabout 1.27 millimeters to about 1.65 millimeters), and having a length L(e.g., as shown in FIG. 2) that is approximately 25 cm. The elongatebody 102 can include a pointed distal tip 104 configured to puncturetissue to facilitate introduction of the device into a target volume oftissue, however, in other embodiments the tip can be blunt and can havevarious other configurations. The elongate body 102 can be formed from aconductive material such that the elongate body can conduct electricalenergy along its length to one or more ablation elements located along adistal portion of the elongate body. Emitter electrode 105 is an exampleof an ablation element capable of delivering RF energy from the elongatebody.

In some embodiments, the emitter electrode 105 can be a portion of theelongate body 102. For example, the elongate body 102 can be coated inan insulating material along its entire length except for the portionrepresenting the emitter electrode 105. More particularly, in oneembodiment, the elongate body 102 can be coated in 1.5 mil of thefluoropolymer Xylan™ 8840. The electrode 105 can have a variety oflengths and shape configurations. In one embodiment, the electrode 105can be a 4 mm section of a tubular elongate body that is exposed tosurrounding tissue. Further, the electrode 105 can be located anywherealong the length of the elongate body 105 (and there can also be morethan one electrode disposed along the length of the elongate body). Inone embodiment, the electrode can be located adjacent to the distal tip104. In other embodiments, the elongate body can be formed from aninsulating material, and the electrode can be disposed around theelongate body or between portions of the elongate body.

In other embodiments, the electrode can be formed from a variety ofother materials suitable for conducting current. Any metal or metal saltmay be used. Aside from stainless steel, exemplary metals includeplatinum, gold, or silver, and exemplary metal salts includesilver/silver chloride. In one embodiment, the electrode can be formedfrom silver/silver chloride. It is known that metal electrodes assume avoltage potential different from that of surrounding tissue and/orliquid. Passing a current through this voltage difference can result inenergy dissipation at the electrode/tissue interface, which canexacerbate excessive heating of the tissue near the electrodes. Oneadvantage of using a metal salt such as silver/silver chloride is thatit has a high exchange current density. As a result, a large amount ofcurrent can be passed through such an electrode into tissue with only asmall voltage drop, thereby minimizing energy dissipation at thisinterface. Thus, an electrode formed from a metal salt such assilver/silver chloride can reduce excessive energy generation at thetissue interface and thereby produce a more desirable therapeutictemperature profile, even where there is no liquid flow about theelectrode.

The electrode 105 or other ablation element can include one or moreoutlet ports 108 that are configured to deliver fluid from an innerlumen 106 extending through the elongate body 102 into surroundingtissue (as shown by arrows 109). Alternatively, the electrode 105 can bepositioned near one or more outlet ports 108 formed in the elongate body102. In many embodiments, it can be desirable to position the electrodeadjacent to the one or more outlet ports to maximize the effect of theflowing fluid on the therapy. The outlet ports 108 can be formed in avariety of sizes, numbers, and pattern configurations. In addition, theoutlet ports 108 can be configured to direct fluid in a variety ofdirections with respect to the elongate body 102. These can include thenormal orientation (i.e., perpendicular to the elongate body surface)shown by arrows 109 in FIG. 1, as well as orientations directedproximally and distally along a longitudinal axis of the elongate body102, including various orientations that develop a circular or spiralflow of liquid around the elongate body. Still further, in someembodiments, the elongate body 102 can be formed with an open distal endthat serves as an outlet port. By way of example, in one embodiment,twenty-four equally-spaced outlet ports 108 having a diameter of about0.4 mm can be created around the circumference of the electrode 105using Electrical Discharge Machining (EDM). One skilled in the art willappreciate that additional manufacturing methods are available to createthe outlet ports 108. In addition, in some embodiments, the outlet portscan be disposed along a portion of the elongate body adjacent to theelectrode, rather than being disposed in the electrode itself.

The inner lumen 106 that communicates with the outlet ports 108 can alsohouse a heating assembly 110 configured to heat fluid as it passesthrough the inner lumen 106 just prior to being introduced into tissue.Furthermore, the portion of the elongate body located distal to theelectrode 105 or other ablation element can be solid or filled such thatthe inner lumen 106 terminates at the distal end of the electrode 105.In one embodiment, the inner volume of the portion of the elongate bodydistal to the electrode is filled with a plastic plug that can beepoxied in place or held by an interference fit. In other embodiments,the portion of the elongate body distal to the electrode can be formedfrom solid metal and attached to the proximal portion of the elongatebody by welding, swaging, or any other technique known in the art.

Fluid can be supplied to the inner lumen 106 and heating assembly 110from a fluid reservoir 112. The fluid can be at least partiallydegassed, as described in more detail below. In some embodiments, thefluid can be degassed prior to introduction into the reservoir of thesystem, while in some embodiments, such as the embodiment shown in FIG.1, an apparatus 119 for degassing fluid can be incorporated into thesystem, as also described further below. The fluid reservoir 112, andthe degassing apparatus 119 if provided, can be connected to the innerlumen 106 via a fluid conduit 114. The fluid conduit 114 can be, forexample, flexible plastic tubing. The fluid conduit 114 can also be arigid tube, or a combination of rigid and flexible tubing.

Fluid can be urged from the fluid reservoir 112, into the degassingapparatus 119 if provided, and into the inner lumen 106 by a pump 116.The pump 116 can be a syringe-type pump that produces a fixed volumeflow with advancement of a plunger (not shown). An example of such apump is a Model 74900 sold by Cole-Palmer Corporation of Chicago, Ill.Other types of pumps, such as a diaphragm pump, may also be employed.

The pump 116, and/or degassing apparatus 119 if provided, can becontrolled by a power supply and controller 118. The power supply andcontroller 118 can deliver electrical control signals to the pump 116,and/or degassing apparatus 119 if provided, to cause the pump to producea desired flow rate of fluid. The power supply and controller 118 can beconnected to the pump 116 via an electrical connection 120. The powersupply and controller 118 can also be electrically connected to theelongate body 102 via connection 122, and to a collector electrode 124via connection 126. In addition, the power supply and controller 118 canbe connected to one or more of the heating assembly 110, the degassingapparatus 119 if provided, and/or a sensor (not shown) for determiningone or more parameters of the fluid, such as an amount or a percentageof gas in the fluid, if provided, through similar electrical connections(not shown). The pump 116, power source and controller 118, degassingapparatus 119, and other components can generally be considered as partof a control unit for at least partially degassing and pumping fluid toa treatment site.

The collector electrode 124 can have a variety of forms. For example,the collector electrode 124 can be a large electrode located outside apatient's body. In other embodiments, the collector electrode 124 can bea return electrode located elsewhere along the elongate body 102, or itcan be located on a second elongate body introduced into a patient'sbody near the treatment site.

In operation, the power supply and controller 118 can drive the deliveryof fluid through a degassing apparatus, if provided, and into targettissue at a desired flow rate, the heating of the fluid to a desiredtherapeutic temperature, and the delivery of therapeutic ablative energyvia the one or more ablation elements, such as electrode 105. To do so,the power supply and controller 118 can itself comprise a number ofcomponents for generating, regulating, and delivering requiredelectrical control and therapeutic energy signals. For example, thepower supply and controller 118 can include one or more frequencygenerators to create one or more RF signals of a given amplitude andfrequency. These signals can be amplified by one or more RF poweramplifiers into relatively high-voltage, high-amperage signals, e.g., 50volts at 1 amp. These RF signals can be delivered to the ablationelement via one or more electrical connections 122 and the elongate body102 such that RF energy is passed between the emitter electrode 105 andthe collector electrode 124 that can be located remotely on a patient'sbody. In embodiments in which the elongate body is formed fromnon-conductive material, the one or more electrical connections 122 canextend through the inner lumen of the elongate body or along its outersurface to deliver current to the emitter electrode 105. The passage ofRF energy between the ablation element and the collector electrode 124can heat the tissue surrounding the elongate body 102 due to theinherent electrical resistivity of the tissue. The power supply andcontroller 118 can also include a directional coupler to feed a portionof the one or more RF signals to, for example, a power monitor to permitadjustment of the RF signal power to a desired treatment level.

The elongate body 102 illustrated in FIG. 1 can be configured forinsertion into a patient's body in a variety of manners. FIG. 2illustrates one embodiment of a medical device 200 having an elongatebody 202 disposed on a distal end thereof configured for laparoscopic ordirect insertion into a target area of tissue. In addition to theelongate body 202, the device 200 can include a handle 204 to allow anoperator to manipulate the device. The handle 204 can include one ormore electrical connections 206 that connect various components of theelongate body (e.g., the heating assembly and ablation element 205) to,for example, the power supply and controller 118 and the degassingapparatus 119, if provided, described above. The handle 204 can alsoinclude at least one fluid conduit 208 for connecting a fluid source tothe device 200.

While device 200 is one exemplary embodiment of a medical device thatcan be adapted for use in fluid enhanced ablation, a number of otherdevices can also be employed. For example, a very small elongate bodycan be required in treating cardiac dysrhythmias, such as ventriculartachycardia. In such a case, an appropriately sized elongate body canbe, for example, disposed at a distal end of a catheter configured forinsertion into the heart via the circulatory system. In one embodiment,a stainless steel needle body between about 20- and about 25-gauge(i.e., an outer diameter of about 0.5 millimeters to about 0.9millimeters) can be disposed at a distal end of a catheter. The cathetercan have a variety of sizes but, in some embodiments, it can have alength of about 120 cm and a diameter of about 8 French (“French” is aunit of measure used in the catheter industry to describe the size of acatheter and is equal to three times the diameter of the catheter inmillimeters).

Therapeutic Treatment Using Fluid Enhanced Ablation

Ablation generally involves the application of high or low temperaturesto cause the selective necrosis and/or removal of tissue. There is aknown time-temperature relationship in the thermal destruction of tissueaccomplished by ablation. A threshold temperature for causingirreversible thermal damage to tissue is generally accepted to be about41° Celsius (C.). It is also known that the time required to achieve aparticular level of cell necrosis decreases as the treatment temperatureincreases further above 41° C. It is understood that the exacttime/temperature relationship varies by cell type, but that there is ageneral relationship across many cell types that can be used todetermine a desired thermal dose level. This relationship is commonlyreferred to as an equivalent time at 43° C. expressed as:

t _(eq.43° C.) =∫R ^((t(t)-43°)) dt  (1)

where T is the tissue temperature and R is a unit-less indicator oftherapeutic efficiency in a range between 0 and 5 (typically 2 fortemperatures greater than or equal to 43° C., zero for temperaturesbelow 41° C., and 4 for temperatures between 41 and 43° C.), asdescribed in Sapareto S. A. and W. C. Dewey, Int. J. Rad. Onc. Biol.Phys. 10(6):787-800 (1984). This equation and parameter set representsjust one example of the many known methods for computing a thermal dose,and any of methodology can be employed with the methods and devices ofthe present invention. Using equation (1) above, thermal doses in therange of t_(eq,43)° C.=20 minutes to 1 hour are generally accepted astherapeutic although there is some thought that the dose required tokill tissue is dependent on the type of tissue. Thus, therapeutictemperature may refer to any temperature in excess of 41° C., but thedelivered dose and, ultimately, the therapeutic effect are determined bythe temporal history of temperature (i.e., the amount of heating thetissue has previously endured), the type of tissue being heated, andequation (1). For example, Nath, S. and Haines, D. E., Prog. Card. Dis.37(4):185-205 (1995) (Nath et al.) suggest a temperature of 50° C. forone minute as therapeutic, which is an equivalent time at 43° C. of 128minutes with R=2. In addition, for maximum efficiency, the therapeutictemperature should be uniform throughout the tissue being treated sothat the thermal dose is uniformly delivered.

FIG. 3 illustrates the performance profiles of several ablationtechniques by showing a simulated temperature achieved at a givendistance from an ablation element, such as electrode 105. The firstprofile 302 illustrates the performance of RF ablation without the useof fluid enhancement. As shown in the figure, the temperature of thetissue falls very sharply with distance from the electrode. This meansthat within 10 millimeters of the ablation element the temperature ofthe tissue is still approximately body temperature (37° C.), far belowthe therapeutic temperature of 50° C. discussed above. Furthermore, veryclose to the ablation element the temperature is very high, meaning thatthe tissue will more quickly desiccate, or dry up, and char. Once thishappens, the impedance of the tissue rises dramatically, making itdifficult to pass energy to tissue farther away from the ablationelement.

A second tissue temperature profile 304 is associated with a secondprior art system similar to that described in U.S. Pat. No. 5,431,649.In this second system, an electrode is inserted into tissue and impartsa 400 kHz RF current flow of about 525 mA to heat the tissue. Bodytemperature (37° C.) saline solution is simultaneously injected into thetissue at a rate of 10 ml/min. The resulting tissue temperature profile304 is more uniform than profile 302, but the maximum temperatureachieved anywhere is approximately 50° C. Thus, the temperature profile304 exceeds the generally accepted tissue damaging temperature thresholdspecified for one minute of therapy in only a small portion of thetissue. As described above, such a small temperature increment requiressignificant treatment time to achieve any therapeutically meaningfulresults.

A third tissue temperature profile 306 is achieved using the teachingsof the present invention. In the illustrated embodiment, an electrodeformed from silver/silver chloride is inserted into tissue and imparts a480 kHz RF current flow of 525 mA to heat the tissue. Saline solutionheated to 50° C. is simultaneously injected into the tissue at a rate of10 ml/min. The resulting temperature profile 306 is both uniform andsignificantly above the 50° C. therapeutic threshold out to 15millimeters from the electrode. Moreover, because the temperature isuniform within this volume, the thermal dose delivered is also uniformthrough this volume.

The uniform temperature profile seen in FIG. 3 can be achieved by theintroduction of heated fluid into the target tissue during applicationof ablative energy. The fluid convects the heat deeper into the tissue,thereby reducing the charring and impedance change in tissue that occursnear the ablation element, as shown in profile 302. Further, because thefluid is heated to a therapeutic level, it does not act as a heat sinkthat draws down the temperature of the surrounding tissue, as seen inprofile 304. Therefore, the concurrent application of RF energy andperfusion of heated saline solution into the tissue eliminates thedesiccation and/or vaporization of tissue adjacent to the electrode,maintains the effective tissue impedance, and increases the thermaltransport within the tissue being heated with RF energy. The totalvolume of tissue that can be heated to therapeutic temperatures, e.g.,greater than 41° C., is thereby increased. For example, experimentaltesting has demonstrated that a volume of tissue having a diameter ofapproximately 8 centimeters (i.e., a spherical volume of approximately156 cm³) can be treated in 5 minutes using the fluid enhanced ablationtechniques described herein. By comparison, conventional RF can onlytreat volumes having a diameter of approximately 3 centimeters (i.e., aspherical volume of approximately 14 cm³) in the same 5-minute timespan.

In addition, fluid enhanced ablation devices according to the presentinvention have a greater number of parameters that can be varied toadjust the shape of the treatment profile according to the tissue beingtreated. For example, when using the SERF ablation technique, anoperator or control system can modify parameters such as salinetemperature (e.g., from about 40° C. to about 80° C.), saline flow rate(e.g., from about 0 ml/min to about 20 ml/min), the amount of degassingof the saline, RF signal power (e.g., from about 0 W to about 100 W),and duration of treatment (e.g., from about 0 minutes to about 10minutes) to adjust the temperature profile 306 and improve thereproducibility of the therapy. In addition, different electrodeconfigurations can also be used to vary the treatment. For example,although the emitter electrode 105 illustrated in FIG. 1 is configuredas a continuous cylindrical band adapted for a mono-polar current flow,the electrode can also be formed in other geometries, such as sphericalor helical, that form a continuous surface area, or the electrode mayhave a plurality of discrete portions. The electrodes may also beconfigured for bipolar operation, in which one electrode (or a portionof an electrode) acts as a cathode and another electrode (or portionthereof) acts as an anode.

A preferred fluid for use in the SERF ablation technique is sterilenormal saline solution (defined as a salt-containing solution). However,other liquids may be used, including Ringer's solution, or concentratedsaline solution. A fluid can be selected to provide the desiredtherapeutic and physical properties when applied to the target tissueand a sterile fluid is recommended to guard against infection of thetissue. The fluid can be further enhanced by at least partially removinga one or more dissolved gases from the fluid, such that the fluidcontains one or more gases having a predetermined pressure and mixture.In some embodiments, this predetermined pressure and mixture can be lessthan a predetermined value for one or more of the gases. The remainingportions of the description are directed primarily to devices andmethods for degassing fluid used in conjunction with fluid enhancedablation therapy.

Fluid Degassing

Fluids commonly include one or more dissolved gases that can, undercertain conditions, come out of solution in the form of gas bubbles.Exemplary gases commonly dissolved in fluid include oxygen, nitrogen,carbon dioxide, and other gases present in the atmosphere. Dissolvedgases come out of solution according to the ability of a fluid to hold aparticular gas in solution at a given temperature and pressure. Thisrelationship is governed by Henry's Law, which states that at aparticular temperature, the amount of a particular gas that dissolves ina particular type and volume of liquid is proportional to the partialpressure of the gas in equilibrium with the liquid. In other words, theamount of a gas that can be dissolved in a fluid depends on thetemperature of the fluid, the pressure of the gas in the environmentsurrounding the fluid, as well as the type and volume of the fluid. Forexample, water and saline are commonly able to hold less gas in solutionas the temperature of the fluid is increased. The increased kineticenergy of the gas molecules in the solution causes them to more easilyescape the solution, resulting in lowered solubility.

In fluid enhanced ablation, fluid is heated just prior to introductioninto tissue. The heating process reduces the solubility of the dissolvedgases, resulting in one or more gases coming out of solution in the formof gas bubbles. These bubbles can form, for example, inside the innerlumen and can subsequently exit the outlet ports 108 into the tissuesurrounding the elongate body 102. Furthermore, gas bubbles may alsoform just outside the elongate body due to heating from the emitterelectrode 105. Gases that come out of solution during ablation therapycan have a detrimental effect on the control, and therefore theeffectiveness, of the fluid supplied to the treatment site. This isprimarily because the gas bubbles formed in the fluid are compressible,while the fluid itself is not. This compressibility, or compliance, isundesirable in a fluid enhanced ablation system. For example, a pump canbe designed to advance a plunger on a fluid-filled syringe at aparticular speed so as to induce a particular flow rate. As long as thefluid path contains only incompressible fluid, the flow rate can bemaintained as a constant despite changes in back-pressure that can becaused by physiologic changes in the tissue, or by changes in fluidresistivity due to ablation therapy. However, if the fluid containscompressible gas bubbles, an increase in back-pressure from the tissuemay alter the flow rate because the changing pressure can, at least inpart, be absorbed by the compressible gas bubbles. Accordingly, anypossible compliance of the fluid used in fluid enhanced ablation therapyshould be reduced. This can be accomplished, for example, by removing atleast some of the dissolved gas in the fluid. Removing dissolved gasfrom the fluid can increase the temperature at which gas comes out ofsolution, thereby reducing the compliance of a fluid enhanced ablationsystem in which the fluid is used. Using degassed fluids can increasethe effectiveness, reproducibility, and overall reliability of fluidenhanced ablation systems.

Gas can be removed from the fluid in a variety of ways, some of whichare described in greater detail below. These methods include degassingusing one or more chemicals, boiling the fluid, exposing the fluid to avacuum, and exposing the fluid to a gas having a desired gasconcentration. While methods to remove gas from the fluid can be appliedto remove substantially all of the gas within the fluid, in someembodiments it can be desirable to maintain some of the gas in thefluid. For example, in some instances it may be desirable to maintainsome level of oxygen in the fluid or some level of carbon dioxide in thefluid. By way of non-limiting example, in one embodiment, it can bedesirable to degas a fluid to a partial pressure of oxygen (O₂) in arange of about 20 mm to about 40 mm of mercury. These levels of oxygencan prevent the complete oxygen deprivation of tissues being treatedwith fluid enhanced ablation. Accordingly, the devices and methods ofthe present invention can be utilized to at least partially degas afluid such that the fluid contains a predetermined concentration of aparticular gas. In some embodiments, this can be accomplished bydegassing a fluid such that the fluid contains less than a predeterminedpartial pressure of a particular gas. The predetermined partial pressurecan be set as desired by a user.

Chemical degassing can be performed by adding one or more chemicals tothe fluid that bind or otherwise react with dissolved gases within thefluid. The chemicals can be formulated or configured to remove one ormore gases from the fluid. A person skilled in the art will recognizevarious chemicals or groups of chemicals that can target and remove oneor more gases from the fluid. For example, oxygen can be selectivelyremoved from a fluid by introducing a reductant, such as ammoniumsulfite, into the fluid.

Degassing a fluid by boiling can be performed by heating the fluid for aperiod of time up to or above a temperature that can cause one or moregases to be removed. As the fluid heats up, its ability to hold gas insolution will decrease, and the gases within the fluid can begin to comeout of solution and dissipate from the system. By way of example only, avolume of degassed saline having a desired salinity can be created bystarting with diluted saline (e.g., saline diluted with water) andboiling the diluted saline until the remaining liquid has a desiredsalinity.

Boiling a fluid can be effective to remove a portion of all gasseswithin the fluid. Specific gases, however, can be more difficult totarget using this method because the application of heat to the fluidcan act on all gases within the fluid. However, different gasses candissipate at different rates at the same temperature. Thus, selectivelycontrolling the heating of a fluid can be effective to at leastpartially target the removal of a particular gas from the fluid. Thefluid can be heated or boiled for any amount of time, depending at leastin part on the desired percent gas concentration and the temperature towhich the fluid is heated, however, in some embodiments the fluid can beheated to its boiling point for about 30 minutes.

An additional method for degassing a fluid includes exposing the fluidto a vacuum source, i.e., applying a vacuum to the fluid. Similar toboiling, applying a vacuum to a fluid can be effective to remove aportion of all gases within the fluid. While exemplary apparatuses forapplying a vacuum to fluid are described in greater detail below,including apparatuses such as mass exchangers, a vacuum source cangenerally draw gas from the fluid by reducing the atmospheric pressuresurrounding the fluid, thereby drawing gas out of solution byequilibration forces. For instance, the fluid can be in a chamber and avacuum source can be coupled to the chamber so that the vacuum sourcecan apply a vacuum to the fluid within the chamber. The fluid can beexposed to a vacuum for any amount of time, depending at least in parton the desired percent gas concentration and a strength of the vacuumforce applied to the fluid, however, in some embodiments the fluid canbe exposed to a vacuum for at least about eight hours. This process canbe accelerated by agitating the liquid while exposed to the vacuum tocause cavitation or to increase the surface area of the liquidcontacting the vacuum.

Yet a further method for degassing a fluid includes exposing the fluidto one or more gas sources that contain a gas having a desired gasconcentration, i.e., applying one or more gasses to the fluid. This is avariation on the vacuum concept, in which a vacuum (or “negative”) gassource is employed to draw gas out of solution. By exposing a fluid to aparticular concentration of gas for a period of time, the concentrationof gas in the fluid can begin to equilibrate with the gas source so thatthe percentage of gas in the fluid approaches, and can eventually equal,the percentage of gas present in the gas source. Some exemplaryapparatuses for applying a gas to a fluid are described in greaterdetail below, including mass exchangers. In some embodiments, the fluidcan be in a chamber and a gas source can be coupled to the chamber sothat the gas source can be in fluid communication with the chamber. Whenthe fluid is within a chamber and gas is applied thereto, the chambercan be vented to allow excess gas that comes out of solution to escape.Further, the fluid and/or the gas being applied to the fluid can beagitated to speed up the equilibration process. A person skilled in theart will recognize a number of different ways by which agitation can beimparted on the system, for example, by applying a rotational force toeither or both of the fluid chamber and the gas chamber.

A gas source applied to a fluid can contain a given concentration of asingle gas, or a combination of a plurality of gases at particularpartial pressures. Multiple gases can be applied to the fluid at thesame time or in succession to achieve a desired concentration of one ormore gases within the fluid. The fluid can be exposed to one or more ofthe gas sources for any amount of time, depending at least in part onthe desired gas concentrations within the fluid and the gasconcentrations of the applied gas. For example, in some embodiments thefluid can be exposed to a gas including a partial pressure of oxygenbetween about 20 mm and about 40 mm of mercury. As described above,exposing the fluid to such a gas can result in the fluid equilibratinguntil the fluid contains a partial pressure of oxygen that is alsobetween about 20 mm and about 40 mm of mercury. Other gas sources can beutilized as well, or a single gas source having a predeterminedconcentration and mixture of a plurality of gases can be utilized. Forexample, in some embodiments it can be desirable to utilize a gas sourcethat includes not only oxygen, but also carbon dioxide, as it can aid inmaintaining the pH of the fluid. In such an embodiment, a gas sourcethat includes a partial pressure of carbon dioxide between about 35 andabout 40 mm of mercury can be utilized as a gas source.

Degassing in the Ablation Process

Fluid degassing can be performed at a number of different times inconjunction with fluid enhanced ablation therapy. In some embodiments,the fluid can be degassed prior to delivering the fluid into areservoir. In such embodiments, the fluid can be degassed and theninserted into the fluid reservoir. Fluid degassed prior to introductioninto the fluid reservoir can be sealed in an airtight container toprevent gas from re-entering into solution. Alternatively, the fluid canbe degassed while in the fluid reservoir. In some embodiments, a fluidreservoir containing fluid that is at least partially degassed can beprovided in a sterile container and/or can be pre-packaged in sterilepackaging. The container can then be coupled to a fluid enhancedablation therapy system. For example, degassed fluid can be loaded in asyringe and pre-packaged for use with a fluid enhanced ablation therapysystem. In such embodiments, a sensor can be provided to gauge theconcentration of a gas in a fluid. Gauging the concentration of a gas ina sealed fluid reservoir can be desirable to ensure that a faulty sealhas not allowed gas to re-enter into solution in the fluid. Exemplarysensors are discussed in more detail below.

Alternatively, an apparatus for degassing fluid as shown in FIG. 1 canbe provided in conjunction with the fluid enhanced ablation therapysystem. The fluid reservoir 112 can provide fluid to the degassingapparatus 119, the apparatus 119 can degas the fluid flowingtherethrough using the methods described herein or other methods fordegassing fluid, and then the fluid can flow through the conduit 114 andinto the elongate body 102 for use in ablation. In still furtheralternative embodiments, the degassing apparatus 119 can be disposedupstream of the fluid reservoir 112 such that fluid is supplied from aninitial source (not shown), passed through the degassing apparatus 119for purposes of degassing the fluid, and the fluid can then be stored inthe fluid reservoir 112 for use proximate to the treatment site asdescribed above. Some exemplary embodiments of apparatuses for use indegassing fluid are described in greater detail below.

Effects of Saline Degassing

FIG. 4 illustrates the performance profiles of saline that was notdegassed (labeled as “regular saline”) and saline that was at leastpartially degassed. To produce the results shown in FIG. 4, degassedsaline was obtained by boiling 600 ml of regular saline and 200 ml ofpure water together for approximately 30 minutes. The boiling wasallowed to continue until 600 ml of saline remained. The hot saline wasthen sealed in a flask and cooled. This created a partial vacuum, whichhelped to prevent atmospheric gas from dissolving back into the newlydegassed saline. This procedure produced 600 ml of saline with measureddissolved oxygen levels of approximately 1 mg/L. The same saline, atequilibrium at room temperature and pressure, typically containsapproximately 8 mg/L of dissolved oxygen.

The chart shows the approximate diameter of lesions created using salinewith the two different concentrations of dissolved gas at differenttherapy settings of saline temperature and RF power level. Theexperiments for the two saline gas concentrations involved a 10 ml/minrate of flow and each experiment was replicated five times. The resultsillustrate the mean lesion diameter for various temperatures and powerlevels, and the standard deviation for the same. As shown, the degassedsaline allows for lesions of larger diameters to be achieved across arange of temperature and power levels. As the amount of RF powerincreases and/or saline temperature increases—both conditions underwhich gas is more likely to come out of solution—the disparity increasesbetween the lesion sizes created with degassed saline and those createdwith regular saline. The degassed saline shows an ability toconsistently achieve larger and less variable lesion diameters.Accordingly, the use of at least partially degassed saline in fluidenhanced ablation therapy can contribute significantly to thereliability and effectiveness of the treatment, especially at higherpower levels and temperatures.

Apparatuses for Degassing Fluid

Just as fluid can be degassed in a variety of manners, a number ofdifferent apparatuses can be used to degas fluid. Exemplary apparatusescan include a container or chamber in which the fluid is disposed andthe degassing methods discussed above applied directly thereto (e.g.,applying a chemical, vacuum, or gas to the chamber and/or heating thechamber as described above), or the apparatus can be more elaborate,such as a mass exchanger. An exemplary mass exchanger is the Cell-Pharm®Hollow-Fiber Oxygenator manufactured by CD Medical. One exemplaryembodiment of an apparatus 310 for use in degassing fluid is illustratedin FIGS. 5-7.

The apparatus 310 shown in FIGS. 5-7 is a mass exchanger having aplurality of tubes 330 that are gas permeable and substantially fluidimpermeable. The apparatus 310 can include an inlet 312 for receivingfluid to be treated (i.e., have at least a portion of gas removedtherefrom), an outlet 314 for ejecting treated fluid, and a treatmentchamber 316 disposed therebetween. The treatment chamber 316 can includeone or more tubes 330 in fluid communication with the inlet 312 and theoutlet 314 such that fluid can flow from the inlet 312, through thetubes 330, and out of the outlet 314. In the illustrated embodiment, thetubes 330 are disposed at each end in proximal and distal discs 320,322. The proximal disc 320 can block fluid from flowing through thetreatment chamber 316 such that fluid that enters through the inlet 312can only pass through the chamber 316 via the tubes 330. Likewise, thedistal disc 322 can prevent fluid that passes across the chamber 316 viathe tubes 330 from back-flowing into the chamber 316.

One or more gas outlets or ports 340, 342 can be part of the chamber316. The gas ports 340, 342 can allow various components, such as avacuum source 350 (FIG. 6) or a gas source 360 (FIG. 7), to be connectedto the treatment chamber 316 such that that the components 350, 360 canbe in fluid communication with the treatment chamber 316. The gassources 350, 360 can then be operated as described herein to at leastpartially degas the fluid. The ports 340, 342 can be selectively openedand closed based on a desired treatment of the fluid flowing through thetubes 330. In some embodiments, a sensor 370 for determining at leastone parameter of a fluid flowing through the apparatus 310 can bedisposed at or proximate to the outlet 314. The sensor 370 can beconfigured to measure any number of parameters, but in some exemplaryembodiments the sensor 370 can be configured to measure a concentrationof gas in a fluid passing through the outlet 314.

A housing 318 of the apparatus 310, in which the treatment chamber 316is disposed, can be sized and shaped in any number of ways so that fluidcan flow therethrough while at least a portion of a gas dissolved withinthe fluid can be removed. As shown in the figure, the housing 318 isgenerally cylindrical and is sized to allow the plurality of tubes 330to be spatially disposed therein. The housing 318 can be larger than therespective inlet 312 and outlet 314 disposed near the proximal anddistal ends 318 p, 318 d of the housing 318, as shown, or the housingcan have the same or a smaller outer diameter than the inlet and/oroutlet. The inlet 312 and the outlet 314 can likewise be sized andshaped in any number of ways, and as shown they are generallycylindrical and sized to allow fluid to flow therethrough. One skilledin the art will appreciate that the dimensions of any of thesecomponents can vary depending on the location of the apparatus in thefluid delivery system.

The one or more tubes 330 disposed in the treatment chamber 316 can begas permeable and substantially fluid impermeable. Thus, fluid thatenters the tubes 330 can generally flow through the tubes 330, whilegases disposed in the fluid can dissipate out of the tubes 330 whenparticular environments are produced within the treatment chamber 316(e.g., by the application of a vacuum or other gas source). Manydifferent materials can be used to form gas permeable and substantiallyfluid impermeable walls, including, for example, microporouspolyethylene fibers or expanded polytetrafluoroethylene (PTFE), such asis available from W.L. Gore & Associates, Inc. The tubes 330 can besized and shaped in any number of ways, but as shown the tubes 330 aregenerally elongate, extend substantially across a length of thetreatment chamber 316, and are substantially cylindrical in shape. Spacecan be provided between the tubes 330 so that gas removed from fluidflowing through the tubes 330 can dissipate into the treatment chamber316 and possibly out of one of the gas ports 340, 342, discussed in moredetail below. Any number of tubes 330 can be used, with the flow rate ofthe fluid being based, at least in part, on the number and diameter ofthe tubes 330.

The discs 320, 322 can be configured in a manner that allows thetreatment chamber 316 to be separated from the inlet 312 and outlet 314.Thus, fluid entering the inlet 312 can generally only flow across thetreatment chamber 316 by passing through the tubes 330 and cannotgenerally enter the chamber 316 through the inlet 312 or by back-flowinginto the chamber 316 near the outlet 314. Accordingly, a diameter of thediscs 320, 322 can be substantially equal to an inner diameter of thehousing 318 at the proximal and distal ends 318 p, 318 d of the housing318. Further, a connection between the ends of the tubes 330 and thediscs 320, 322 in which the tubes 330 can be disposed can generally befluid-tight such that fluid cannot generally flow into the chamber 316between the tubes 330 and the respective disc 320, 322. While a varietyof materials can be used to form the discs 320, 322, in one exemplaryembodiment an epoxy is used to form the discs 320, 322.

The gas ports 340, 342 can generally be configured to allow a vacuum orgas to be applied to the treatment chamber 316 between the proximal anddistal discs 320, 322. Thus, the ports 340, 342 can be in fluidcommunication with the treatment chamber 316. In the embodiment shown inFIG. 5, the ports 340, 342 are open, but in one exemplary use, shown inFIG. 6, a vacuum source 350 can be coupled to one of the ports 342 andthe other port 340 can be closed so that a vacuum can be created withinthe treatment chamber 316. Applying a vacuum to the treatment chamber316 can draw gas from fluid passing through the tubes 330 through thegas-permeable walls of the tubes 330 and into the treatment chamber 316.As discussed above, the vacuum source 350 can be applied to create adesired percent concentration of gas in the fluid passing through thetubes 330.

In another exemplary use of the ports 340, 342, shown in FIG. 7, a gassource 360 can be coupled to one of the ports 342 and the other port 342can remain open. The gas source 360 can have a desired concentrationlevel of one or more particular gases. As the gas is supplied to thetreatment chamber 316, the gas in the chamber 316 and the gas in thefluid can begin to equilibrate. Excess gas from the fluid can dissipateout of the fluid, through the gas-permeable walls of the tubes 330, andinto the chamber 316. As the system continues to equilibrate, excess gascan flow out of the open gas port 342, thus creating a substantiallyuniform percent concentration of gas in the fluid flowing through thetubes 330 and the chamber 316. As described above, any number of gasescan be supplied simultaneously or consecutively to achieve variouspercent concentrations of gas in the fluid.

The sensor 370 at the distal end of the apparatus 310 can be any numberof sensors and it can be configured to measure any number of parametersof the system. In one exemplary embodiment, the sensor 370 can beconfigured to measure a percent concentration of gas in a fluid locatedproximate to the outlet 314. For example, the sensor 370 can be anoxygen sensor. While the sensor 370 is shown in the distal end 318 d ofthe housing 318, in other embodiments one or more sensors 370 can bedisposed in other locations of the apparatus 310, or in other portionsof the system. By way of non-limiting example, a sensor for measuringparameters such as the percent concentration of gas in a fluid can bedisposed in the elongate body 102, proximate to the treatment site (FIG.1).

While sample shapes and sizes are provided herein for the variouscomponents of the apparatus 310, a person skilled in the art willrecognize that the size and shape of the apparatus 310 and itscomponents can depend on a number of factors, including, at least inpart, the size and shape of the other components. For example, a size ofthe components of the degassing apparatus 310 that is used inconjunction with a fluid enhanced ablation therapy system can be sizedrelative to the other fluid enhanced ablation therapy system components,while a size of the components of the degassing apparatus 310 that isused to degas the fluid prior to associating a fluid reservoir with thefluid enhanced ablation therapy system can be larger because its sizedoes not need to generally account for the size of other components ofthe fluid enhanced ablation therapy system.

Integration Into Ablation Systems

In embodiments in which the fluid is degassed separately from the fluidenhanced ablation system, the system can operate in a manner asdescribed with respect to FIG. 1 but with the degassing apparatus 119being separate from the system. The fluid can be degassed in any numberof manners as described herein or otherwise known in the art, and thenit can be coupled to or delivered into the fluid enhanced ablationsystem for application proximate to the treatment site. In embodimentsin which the fluid is degassed as part of the fluid enhanced ablationtherapy system, the system can operate in a manner similar as describedwith respect to FIG. 1. The degassing apparatus 310, or equivalentsthereof, can be supplied as the degassing apparatus 119 of FIG. 1.Accordingly, fluid can be pumped from the fluid reservoir 112 by thepump 116 into the inlet 312 of the degassing apparatus 310. The fluidcan then pass across the treatment chamber 316 via the tubes 330 andinto the outlet 314. As the fluid flows through the tubes 330, degassingforces, such as a force supplied by a vacuum source and/or another gassource, can be applied to the fluid so that gas can be selectivelyremoved from the fluid in the tubes 330. Fluid from the outlet can thencontinue to be pumped by the pump 116 into the conduit 114 forapplication proximate to the treatment site.

Methods of Use

As described above, the various embodiments of the devices and systemsdisclosed herein can be utilized in a variety of surgical procedures totreat a number of medical conditions. For example, medical devices asdisclosed herein can be configured for insertion into a target volume oftissue directly during an open surgical procedure or during percutaneousablation therapy. Alternatively, the medical devices can be configuredto be passed through one or more layers of tissue during a laparoscopicor other minimally invasive procedure. Furthermore, the devices can beconfigured for introduction into a patient via an access port or otheropening formed through one or more layers of tissue, or via a naturalorifice (i.e., endoscopically). Depending on the device employed,delivery may be facilitated by directly inserting the elongate body asshown in FIG. 2, or by introducing a catheter containing an elongatebody through, for example, a patient's circulatory system. Followingdelivery to a treatment site, a portion of a surgical device, e.g., adistal portion of the elongate body 102, can be inserted into a targettreatment volume such that an ablation element is disposed within thetreatment volume. In some embodiments, the ablation element can bepositioned near the center of the treatment volume.

Once the device is positioned within the treatment volume, fluid can bedelivered through the device into the treatment volume. The heatingassemblies disclosed herein can be utilized to deliver fluid, such asthe at least partially degassed fluid disclosed herein, at a therapeutictemperature, as described above. Alternatively, in some embodiments, thefluid can be delivered without first being heated to a therapeutictemperature. The fluid introduced into the target volume of tissue canbe degassed on demand (e.g., as it flows from a reservoir to thetreatment volume) by, for example, a degassing apparatus as describedabove, or can be degassed prior to storage in the fluid reservoir.Furthermore, the amount of degassing can be tested using, for example, asensor either prior to or during ablation therapy. In addition todelivering fluid to the treatment volume, one or more ablation elementscan be activated to simultaneously deliver therapeutic energy, such asRF energy, into the tissue in the treatment volume. In some embodiments,however, the one or more ablation elements need not be activated, andtherapy can be administered by delivering therapeutically heated fluidfrom the elongate body alone. After a period of time, or depending onone or more feedback indications (e.g., a reading from a temperaturesensor disposed within the treatment volume), the ablation element canbe deactivated and the flow of fluid into the volume can be stopped. Thedevice can then be removed and/or repositioned if additional therapy isrequired.

In other embodiments, degassed fluid can also be utilized with othertypes of ablation procedures. For example, unheated degassed fluid canbe introduced through a conventional shower-head ablation electrode thatis configured to contact, but not penetrate, a treatment volume. The useof a degassed fluid can still be advantageous when utilizing unheatedfluid because the fluid can still experience heating in the vicinity ofthe ablation element.

Sterilization and Reuse

The devices disclosed herein can be designed to be disposed after asingle use, or they can be designed for multiple uses. In either case,however, the device can be reconditioned for reuse after at least oneuse. Reconditioning can include any combination of the steps ofdisassembly of the device, followed by cleaning or replacement ofparticular pieces, and subsequent reassembly. In particular, the devicecan be disassembled, and any number of the particular pieces or parts ofthe device can be selectively replaced or removed in any combination.Upon cleaning and/or replacement of particular parts, the device can bereassembled for subsequent use either at a reconditioning facility or bya surgical team immediately prior to a surgical procedure. Those skilledin the art will appreciate that reconditioning of a device can utilize avariety of techniques for disassembly, cleaning/replacement, andreassembly. Use of such techniques, and the resulting reconditioneddevice, are all within the scope of the present invention.

For example, the surgical devices disclosed herein may be disassembledpartially or completely. In particular, the elongate body 202 of themedical device 200 shown in FIG. 2 may be removed from the handle 204,or the entire handle and elongate body assembly may be decoupled fromthe electrical and fluid connections 206, 208. In yet anotherembodiment, the handle, elongate body, and connections may be removablycoupled to a housing that contains, for example, the fluid reservoir,degassing apparatus, pump, and power supply and controller shown in FIG.1.

Further, the degassing apparatuses described herein may also bedisassembled partially or completely. In particular, a degassingapparatus similar to the apparatus 310 can be disconnected from a fluidenhanced ablation system and cleaned or otherwise sterilized by, forexample, passing a cleaning fluid through the apparatus. Still further,in some embodiments, the apparatus can be configured to disassemble suchthat individual components, such as each tube 330, can be removed andcleaned individually, or replaced.

Preferably, the devices described herein will be processed beforesurgery. First, a new or used instrument can be obtained and, ifnecessary, cleaned. The instrument can then be sterilized. In onesterilization technique, the instrument is placed in a closed and sealedcontainer, such as a plastic or TYVEK bag. The container and itscontents can then be placed in a field of radiation that can penetratethe container, such as gamma radiation, x-rays, or high-energyelectrons. The radiation can kill bacteria on the instrument and in thecontainer. The sterilized instrument can then be stored in the sterilecontainer. The sealed container can keep the instrument sterile until itis opened in the medical facility.

In many embodiments, it is preferred that the device is sterilized. Thiscan be done by any number of ways known to those skilled in the artincluding beta or gamma radiation, ethylene oxide, steam, and a liquidbath (e.g., cold soak). In certain embodiments, the materials selectedfor use in forming components such as the elongate body may not be ableto withstand certain forms of sterilization, such as gamma radiation. Insuch a case, suitable alternative forms of sterilization can be used,such as ethylene oxide.

One skilled in the art will appreciate further features and advantagesof the invention based on the above-described embodiments. Accordingly,the invention is not to be limited by what has been particularly shownand described, except as indicated by the appended claims. Allpublications and references cited herein are expressly incorporatedherein by reference in their entirety.

What is claimed is:
 1. An ablation system, comprising: an elongate bodyhaving proximal and distal ends, an inner lumen extending through theelongate body, and at least one outlet port formed in the elongate bodyconfigured to deliver fluid to tissue surrounding the elongate body; anablation element disposed along a length of the elongate body adjacentto the at least one outlet port, the ablation element being configuredto heat tissue surrounding the ablation element when the elongate bodyis inserted into tissue; a heating assembly disposed within the innerlumen adjacent to the ablation element, the heating assembly beingconfigured to heat fluid flowing through the inner lumen; and a fluidsource in fluid communication with the inner lumen for delivering fluidthrough the inner lumen, the fluid source containing a volume of fluidthat is at least partially degassed such that the fluid contains one ormore gases having a predetermined pressure and mixture.
 2. The system ofclaim 1, further comprising a pump coupled to the fluid source andconfigured to pump fluid from the fluid source through the inner lumenof the elongate body.
 3. The system of claim 1, further comprising amass exchanger coupled to the fluid source and configured to at leastpartially degas the fluid.
 4. The system of claim 1, wherein the fluidsource comprises a syringe configured to couple to the elongate body fordelivering fluid to the inner lumen.
 5. The system of claim 1, whereinthe fluid comprises saline.
 6. The system of claim 1, further comprisinga sensor configured to measure an amount of the gas in the fluid.
 7. Anablation system, comprising: an elongate body having proximal and distalends, an inner lumen extending through the elongate body, and at leastone outlet port formed in the elongate body configured to deliver fluidto tissue surrounding the elongate body; an ablation element disposedalong a length of the elongate body adjacent to the at least one outletport, the ablation element being configured to heat tissue surroundingthe ablation element when the elongate body is inserted into tissue; aheating assembly disposed within the inner lumen adjacent to theablation element, the heating assembly being configured to heat fluidflowing through the inner lumen; and a mass exchanger in fluidcommunication with fluid flowing through the inner lumen, the massexchanger being configured to at least partially degas fluid flowingthrough the inner lumen.
 8. The system of claim 7, wherein the massexchanger includes a plurality of gas-permeable and fluid-impermeabletubes, and at least one outlet configured to couple to a gas source foradjusting the amount of a gas in the fluid flowing through the pluralityof gas-permeable and fluid-impermeable tubes.
 9. The system of claim 7,wherein the gas source comprises a vacuum source for removing gas fromthe fluid.
 10. The system of claim 7, wherein the gas source comprises avolume of one or more gases having a predetermined pressure and mixture.11. The system of claim 7, wherein the mass exchanger is disposedproximal of the heating assembly such that fluid is at least partiallydegassed before being heated by the heating assembly.
 12. The system ofclaim 7, wherein the mass exchanger is disposed within a control unitcoupled to a proximal end of the elongate body, the control unit havinga pump effective to pump fluid from a fluid source, through the massexchanger, and into the inner lumen of the elongate body.
 13. The systemof claim 7, further comprising a sensor configured to measure an amountof a gas in fluid after it flows through the mass exchanger.
 14. Amethod for ablating tissue, comprising: inserting an elongate body intoa tissue mass; delivering through an inner lumen of the elongate bodyfluid that is at least partially degassed such that the fluid containsone or more gases having a predetermined pressure and mixture;delivering energy to at least one heating assembly disposed within theinner lumen to heat the at least partially degassed fluid within thelumen such that the at least partially degassed fluid flows through atleast one outlet port in the elongate body and into the tissue mass; anddelivering energy to an ablation element, while simultaneouslydelivering energy to the at least one heating assembly, to ablate thetissue mass.
 15. The method of claim 14, further comprising, prior todelivering the at least partially degassed fluid through the innerlumen, activating a pump to deliver fluid through a mass exchanger thatat least partially degasses the fluid, the at least partially degassedfluid flowing from the mass exchanger into the inner lumen of theelongate body.
 16. The method of claim 14, wherein delivering the atleast partially degassed fluid through an inner lumen comprisesinjecting the at least partially degassed fluid into a control unit, andactivating a pump to cause the pump to force the at least partiallydegassed fluid through the inner lumen.
 17. The method of claim 14,wherein the fluid comprises saline.
 18. The method of claim 14, furthercomprising, prior to delivering at least partially degassed fluidthrough the inner lumen of the elongate body, determining an amount of agas in the at least partially degassed fluid with a sensor.